Ball Grid Arrays (BGA) and Column Grid Arrays (CGA) are widely used to electrically and mechanically connect substrates (typically ceramic) having semiconductor chips to a card. The BGA commonly comprises an array of metal balls that are soldered to the substrate utilizing a solder fillet material. The solder fillet material typically has a lower melting temperature (183xc2x0 C. for eutectic Pb/Sn) than the solder ball (300xc2x0 C.) to which it joins to, enabling the solder ball to be joined with the substrate without melting. In some instances, however, the solder ball and solder fillet material are of the same composition, thus causing the entire interconnect to become liquidous during the reflow. During the above manufacturing process to form a module, a defect may occur to one or more balls which requires the array of balls to be removed and replaced with a new array of balls.
After the module is populated with interconnects, such as a BGA, the module is typically joined to a card, often with the same solder alloy used initially to join the BGA to the substrate forming the module. Should a defect occur when joining a module to a card or later testing of the card mounted module, the module is removed from the card. When a module is removed from a card, it is necessary to remove the remaining balls and repopulate the substrate with a new array of balls if the module is to be used again.
Not only must the solder balls (or interconnects) be removed if a defect occurs during manufacturing, mounting, or testing a module, but the fillet solder that mechanically retains the interconnects in place must be dressed off in such a manner that new fillet material can be applied.
A conventional method to remove and dress BGA""s from substrates is known as hot oil rework. A module is placed vertically into a chuck and lowered into a bath of oil heated to approximately 220xc2x0 C. The hot oil melts the fillet material holding the balls (interconnects). A wiper blade then pushes against the substrate and wipes off the BGA""s and the fillet material as the wiper is lifted out of the bath. The problems with the above method are twofold. First, the entire substrate must be subjected to the hot oil. The hot oil is detrimental to certain microelectronic components and packaging. Secondly, the use of hot oil to remove components disposed on the top surface that are joined with substantially the same solder alloys as the BGA""s on the bottom surface cause the top surface components to fall off when subjected to a liquidous temperature in the hot oil bath meant only to remove the bottom surface BGA""s. Furthermore, the conventional hot oil process is conducted in a batch mode, as opposed to a more desirable mode of continuously feeding a tool with individual modules needed to be reworked Therefore, the conventional hot oil process cannot ensure the effectiveness of rework, results in undesirable damage to certain microelectronic components and organic carriers, and enables top surface metallurgy components to fall off and must then be repopulated. There thus remains a need for an improved method and apparatus to remove BGA interconnects for rework from substrates and interposers.
The above-described circumstances are overcome and alleviated by the present apparatus and method for removing molten and solid material from a substrate, such as, for example solder and BGA interconnects for rework. One embodiment is a method for removing at least one molten or solid structure from a surface comprising: placing the surface with the at least one molten or solid structure in a fixture; disposing said wiper assembly acted on by a bias proximate the at least one molten or solid structure; retaining the wiper assembly in a first position with a device having a first temperature point level equivalent to or higher than a second melting point level of the at least one molten or solid structure; and raising the temperature of the fixture to the first temperature point level; wherein the at least one molten or solid structure is wiped from the surface when the device reaches the first temperature point level. Another embodiment is an apparatus for removing at least one molten or solid structure from a substrate for rework, the apparatus comprising: a fixture for sustaining and biasing the substrate against a wiper assembly; the wiper assembly configured and positioned to slidably engage at least a portion of the substrate; a heat source to raise the temperature to a melting point level of the at least one molten or solid structure; a bias for translating the wiper assembly along a surface of the substrate having the at least one molten or solid structure to be removed; and a guide block assembly capable of guiding and locking the wiper assembly.